A.I. Explanation:

First sentence: Why this is the first line? This paragraph is the first sentence because it introduces the main topic, which is the formation of our moon. It gives a broad overview of the idea that has been accepted for many years. This follows the rule of Topic Sentence. Why other lines are not chosen? The other paragraphs are not chosen because they do not stand alone. For example, Paragraph 2 starts with "The precursors" which needs context. Paragraph 3 uses "According to" which refers back to a previous idea. Paragraph 4 starts with "In this last collision" which also needs prior information.

Concluding sentence: Why this is the last line? This paragraph is the last sentence because it provides a specific detail that wraps up the discussion about the giant impact hypothesis. It gives a clear example of the collision that led to the formation of the moon, which concludes the topic.

Paragraph pairs:

• Pair 1 (Paragraph 1 → Paragraph 2): Paragraph 2 connects to Paragraph 1 because it gives background information about the bodies involved in the giant impact hypothesis. This follows the Broader to Specific Strategy, where the first paragraph introduces a general idea and the second provides specific details.
• Pair 2 (Paragraph 2 → Paragraph 3): Paragraph 3 connects to Paragraph 2 because it explains how the planetary embryos relate to the formation of the moon. This follows the Logical Order rule, as it continues the discussion about the planetary embryos and their role in the giant impact hypothesis.
• Pair 3 (Paragraph 3 → Paragraph 4): Paragraph 4 connects to Paragraph 3 because it gives a specific example of the last collision mentioned in the giant impact hypothesis. This follows the Topic Example rule, where the second paragraph provides an example that supports the idea in the first.